The continuous shrinking in dimensions of electronic devices utilized in ULSI circuits in recent years has resulted in increasing the resistance of the BEOL metallization as well as increasing the capacitance of the intralayer and interlayer dielectric. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (k) insulators and particularly those with k significantly lower than silicon oxide are needed to reduce the capacitances. Dielectric materials (i.e., dielectrics) that have low k values are commercially available. One such commercially available material, for example, is polytetrafluoroethylene (“PTFE”), which has a dielectric constant of about 2.0. Most commercially available dielectric materials however are not thermally stable when exposed to temperatures above 300° C. Integration of low k dielectrics in present ULSI chips requires a thermal stability of at least 400° C.
The low k materials that have been considered for applications in ULSI devices include polymers containing elements of Si, C, O and H, such as methylsiloxane, methylsilsesquioxanes, and other organic and inorganic polymers. For instance, an article by N. Hacker et al. “Properties of new low dielectric constant spin-on silicon oxide based dielectrics” Mat. Res. Soc. Symp. Proc. 476 (1997); 25 describes materials that appear to satisfy the thermal stability requirement, even though some of these materials propagate cracks easily when reaching thicknesses needed for integration in an interconnect structure when films are prepared by a spin-on technique. Furthermore, these prior art precursor materials are high cost and prohibitive for use in mass production. Moreover, most of the fabrication steps of very large scale integration (“VLSI”) and ULSI chips are carried out by plasma enhanced chemical or physical vapor deposition techniques.
The ability to fabricate a low k material by a plasma enhanced chemical vapor deposition (PECVD) technique using previously installed and available processing equipment will thus simplify its integration in the manufacturing process, reduce manufacturing cost, and create less hazardous waste. U.S. Pat. Nos. 6,147,009 and 6,497,963 describe a low dielectric constant material consisting of elements of Si, C, O and H atoms having a dielectric constant of not more than 3.6 and which exhibits very low crack propagation velocities.
U.S. Pat. Nos. 6,312,793, 6,441,491, 6,541,398 and 6,479,110 B2 describe a multiphase low k dielectric material that consists of a matrix phase composed of elements of Si, C, O and H and another phase composed mainly of C and H. The dielectric materials disclosed in the foregoing patents have a dielectric constant of not more than 3.2.
U.S. Pat. No. 6,437,443 describes a low k dielectric material that has two or more phases wherein the first phase is formed of a SiCOH material. The low k dielectric material is provided by reacting a first precursor gas containing atoms of Si, C, O, and H and at least a second precursor gas containing mainly atoms of C, H, and optionally F, N and O in a plasma enhanced chemical vapor deposition chamber.
Despite the numerous disclosures of low k dielectric materials, there is a continued need to improve the PECVD process in order to improve the properties of the final SiCOH dielectric material. For example, a SiCOH dielectric material having a lower internal stress, improved thermal stability, lower cost and better process control within processing temperatures used in current ULSI technologies are all needed.
It is commonly found that SiCOH dielectric materials made in the prior art from two or more separate organosilicon and/or porogen precursors are not uniform in atomic and structural composition, both when measured across the substrate diameter, and through the depth of the layer. The use of 300 mm Si wafers has made this problem of chemical uniformity across the wafer more pronounced.
It is also commonly found that SiCOH dielectric materials made from two or more separate organosilicon and/or porogen precursors exhibit process variation or process instability due to small changes in the flow rate of one of the two precursors, known as drift in the flow rate.
In view of the above, there is a need to provide a process to fabricate a layer of a SiCOH dielectric material having improved film properties, that is uniform in atomic and structural composition, both when measured across the substrate diameter, and through the depth of the layer, which does not exhibit any variation in the process or process instability.